1. Field of the Invention
The present invention relates to a dual gap horizontal thin film inductive head and more particularly to a horizontal thin film inductive head which employs a dual gap for writing wide and reading narrow.
2. Description of the Related Art
In the magnetic recording arts a magnetic head records a track of information on a magnetic medium, and the same magnetic head or another magnetic head reads the recorded track of information. The magnetic head is mounted on a slider adjacent the magnetic medium, such as a magnetic tape or a magnetic disk. The track width of the magnetic head is important from the standpoint of the density of information that can be recorded and read from a square inch of the magnetic medium. This density, known as "areal density", is a product of track density (tracks per inch, or TPI) and linear density (bits per inch, or BPI, along a track). Track density is dependent upon the width of the sensitive element of the magnetic head, while linear density is dependent upon the gap length between magnetic elements of the magnetic head.
A typical arrangement for recording and playback is a single inductive head. An inductive head has an inductive coil embedded in an insulation stack, the coil and insulation stack being sandwiched between a pair of pole pieces. The pole pieces terminate at an air bearing surface (ABS) in a pair of pole tips which are separated by a gap. Track density is determined by the width of the pole tips at the ABS; linear density is determined by the length of the gap between the pole tips at the ABS. During recording, flux fringes from one pole tip to the other across the gap and magnetizes the magnetic medium to record information. During playback the recorded magnetic fields in the magnetic medium are conducted by the pole tips to the coil where readback voltage is induced.
Track width is the same for both recording and playback. This presents a problem during playback since the pole tips will pick up fields from tracks adjacent the track being read. If the track width of the pole tips could be effectively narrowed during playback this problem would be avoided. Unfortunately, there is currently no way to do this with an inductive magnetic head which performs both recording and playback. One solution has been to provide the magnetic medium with guard bands between the information tracks so that during playback the pole tips of the inductive magnetic head are not influenced by fields from adjacent tracks. However, guard bands occupy area on the magnetic medium, thereby limiting areal density.
Because of the aforementioned problems a basic goal in the magnetic recording arts has been to constrain the magnetic head to write wide information tracks and then to read narrowly within the written information tracks ("write wide and read narrow"). One magnetic head arrangement meeting this goal employs two magnetic heads mounted on a slider, one head being a recording head, with a wide track width, and the other a read head, with a narrow track width. The write head is typically an inductive magnetic head as described above and the read head is typically a magnetoresistive (MR) head. An MR head includes an MR sensor which is positioned between first and second gap layers which are, in turn, sandwiched between first and second shield layers. The MR sensor has a width at the ABS which is less than the width of the pole tips of the inductive write head at the ABS. When the magnetic medium is moved relative to the MR head magnetic fields from information tracks induce changes in the resistance of the MR sensor. A sense current is conducted through the MR sensor exhibits these changes as a playback signal. This arrangement, which is referred to as a "merged" or "piggyback" MR head, obviates the requirement of guard bands. However, a merged MR head has many components which must be accurately aligned in order to perform properly. Consequently, merged MR heads are very complex devices, difficult and expensive to manufacture.
Typically, thin film inductive heads are made and mounted such that their films are either parallel or perpendicular to the recording medium. C. D. Mee, et al., Magnetic Recording Volume 1: Technology, McGraw-Hill, 1987, pp. 316-317. Parallel-film heads, also called "horizontal heads", are coveted for their superior low inductance attribute. In the prior art, merged MR heads with horizontal thin film inductive elements are known (U.S. Pat. No. 5,274,520 is an example). However, at the time of making the invention described and claimed in this patent application, the prior art required that the horizontal inductive head and the MR element be formed in separate fabrication steps, with the result that alignment between the elements was critically hard to maintain. Consequently, either the read or the write function was optimized, requiring a compromise of the other function.
There is a strong felt need for an inductive head arrangement which can write wide and read narrow with fewer components than the merged MR head.